The invention relates to a bearing and driving arrangement for a spinning rotor of an open-end spinning unit including a rotor and a shaft manufactured from steel or the like, which shaft is rotatably carried in a wedge gap formed by pairs of supporting disks having rotor shaft engaging fittings made out of plastic. The rotor shaft is driven by a tangential belt drivingly engageable with the rotor shaft between the pair of supporting disks, the tangential belt being pressed against the shaft.
Bearings and driving arrangements of the above noted kind are disclosed in German Patent (DE-PA) No. 19 01 453 which are suitable for very high rotational speeds of spinning rotors, because it is not the very fast rotating shaft of the spinning rotor that is directly, rotatably supported, but rather the axles of the supporting disks, driven with essentially lower rotational speeds, are directly rotatably supported by roller bearings or the like. Such a bearing and driving arrangement is a very complex dynamic system, because the supporting disks are provided with a spring-like elastic fitting which supports the rotor shaft and also because the tangential belt is elastically or resiliently pressed against the rotor shaft. It is further noted with these type of arrangements that compilations of fiber material and/or impurities within the spinning rotor can occur to eccentrically load the system with respect to the rotating axles/rotating axes of the rotating parts. With bearing arrangements of this type being used in practice at rotor speeds up to 80,000 revolution per minute (RPM), a corresponding high strength/size of the rotor shaft is therefore provided so that the rotational speed is clearly beneath the critical rotational speed (rotational speed inducing harmful resonant harmonic vibrations) of the system. Further, the critical system rotational speed itself is very difficult to determine and it may change incidentally during operation by a fiber material accumulation within the spinning rotor during spinning operations.
Currently, in the rotor spinning industry, rotor speeds of 100,000 RPM are desired which even further increase the indicated problems. Thereby a stronger dimensioning, especially of the rotor shaft, leads not only to a correspondingly greater dimensioning of the supporting disks and the bearings resulting in an increase in material expense, these heavier constructions also lead to a disproportionately greater increase in energy consumption for the operation of the spinning machines.
It is an object of the present invention to provide a bearing and driving arrangement of the type mentioned above which will facilitate operation with a spinning rotor having rotational speeds of 100,000 RPM and more without necessitating an increase in material expense and without disproportionately high energy consumption expenses.
The invention involves the recognition that it is possible to design and operate the spinning unit so that the rotational speed of the spinning rotor is safely above the critical system rotational speed. With the system measurements and arrangements constructed according to preferred embodiments of the invention, it is provided that the critical system rotational speed is so low that the high operational rotational velocity remains sufficiently higher so that even any changes eventually occurring during operation, such as an irregular or non-symmetric deposition of fiber material and accumulation of particle impurities in the rotor do not lead to the danger that resonance phenomena occurs which could lead to a destruction of the rotor and/or the supporting disks.
In preferred embodiments of the invention, the object of attaining a system with a critical system rotational speed sufficiently lower than the high operational speeds (80,000 RPM and greater for the rotor shaft) can be achieved utilizing system parameters along the following lines:
rotor weight--less than 70 g (grams) PA1 rotor inside diameter at fiber collecting groove--30-40 mm (millimeter) PA1 rotor shaft diameter--maximum of 8 mm PA1 distance between supported disk pairs--70-100 mm PA1 distance between rotor center of gravity and closest pair of supporting disks--25-35 mm. PA1 tangential belt pressure on the rotor shaft--20-30 N (Newtons)
An especially advantageous practical preferred embodiment of the invention provides that the rotor is lighter than 70 g (grams), the rotor has a mizimum inside diameter at the collection groove of 36 mm (millimeters), the rotor shaft has a maximum diameter of 8 mm (millimeters), the distance between the pairs of supporting disks is between 80 and 90 mm, the distance between the center of gravity of the rotor and the pair of supporting disks facing the same is approximately about 30 mm, and the pressure or compression force for the tangential belt against the rotor shaft is approximately 25 N (Newtons).
In preferred embodiments of the invention, it is also provided that the distance from the center of the tangential belt to the pair of supporting disks facing (closest to) the rotor is between 25 and 40 percent, preferably about one third of the distance between the pairs of supporting disks themselves. This way the introduction of the pressure or compression force of the tangential belt which is seen as the main cause for a vibration, is so arranged that the danger of sympathetic vibration phenomena is further decreased.
In order to avoid that the running or bearing surfaces of the supporting disks are heated with an increased rotational speed in an inadmissible manner, a further arrangement of the preferred embodiments of the invention provides that the running surfaces of at least the supporting disks of the pair facing the rotor are arranged with a circumferential ring groove. The service life for the fittings of the support disks can thereby essentially be improved, even with high rotational speeds.
In a further feature of preferred embodiments of the invention, it is provided that the shaft of the spinning rotor includes ring bands in the area of the pairs of the supporting disks. Thereby, the position of the rotor with respect to its locations relative to the other operational elements, especially a fiber feed channel and a yarn withdrawal channel of a spinning unit utilizing the system, is dependent upon the diameter of the rotor shaft, so that spinning rotor having a thinner shaft may also be inserted into bearings which are originally designed for a larger dimensioned shaft.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, an embodiment in accordance with the present invention.